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Einstein's theory leads scientists to new planet

WASHINGTON: Astronomers have for the first time discovered an exoplanet using a new method that relies on Einstein's special theory of relativity.

"Einstein's planet", formally known as Kepler-76b, is a "hot Jupiter" that orbits its star every 1.5 days. Its diameter is about 25% more than Jupiter's and it weighs twice as much. It orbits a type F star located about 2,000 light years from Earth in the constellation Cygnus.

The planet is tidally locked to its star, always showing the same face to it, just as the Moon is tidally locked to Earth. As a result, Kepler-76b has a temperature of 1,982 degrees Celsius, said co-author Tsevi Mazeh of Tel Aviv University.

Interestingly, the team found strong evidence that the planet has extremely fast jet stream winds that carry the heat around it. As a result, the hottest point on Kepler-76b isn't the substellar point ("high noon") but a location offset by 16,093.4 km.

This effect has only been observed once before, on HD 189733b, and only in infrared light with the Spitzer Space Telescope. This is the first time optical observations have shown evidence of alien jet stream winds at work. The two most prolific techniques for finding exoplanets are radial velocity (looking for wobbling stars) and transits (looking for dimming stars).

The new method looks for three small effects that occur simultaneously as a planet orbits the star. Einstein's "beaming" effect causes the star to brighten as it moves toward us, tugged by the planet, and dim as it moves away.

The brightening results from photons "piling up" in energy, as well as light getting focused in the direction of the star's motion due to relativistic effects. "This is the first time that this aspect of Einstein's theory of relativity has been used to discover a planet," said co-author Tsevi Mazeh of Tel Aviv University. Although Kepler was designed to find transiting planets, this planet was not identified using the transit method. Instead, it was discovered using a technique first proposed by Avi Loeb of the CfA and his colleague Scott Gaudi (now at Ohio State University) in 2003.

The team looked for signs that the star was stretched into a football shape by gravitational tides from the orbiting planet. The star would appear brighter when we observe the "football" from the side, due to more visible surface area, and fainter when viewed end-on. The third small effect was due to starlight reflected by the planet itself.

Once the new planet was identified, it was confirmed by Latham using radial velocity observations gathered by the TRES spectrograph at Whipple Observatory in Arizona, and by Lev Tal-Or using the SOPHIE spectrograph at the Haute-Provence Observatory in France.